Plant Hybrids and Polyploidization

Chris Tuttle

I've been getting into succulent plants recently both as a hobby and as a muse for project ideas/mechanisms. I am particularly fond of the Crassulaceae and am building an on-the-cheap collection ofSempervivum,Jovibarba,
andSedumas well as a lonelyEcheveriaand a tangle ofGraptopetalum. I am really enjoying watching them grow and propagate, especially from plucked off leaves. All these plants are pretty closely related and diverged from each
other quite recently in evolutionary terms.

There is tremendous diversity in this genus and much gene flow with many interspecific and some intergeneric hybrids in cultivation. As is usual with hybrids the largest
barrier to gene flow comes from unpaired chromosomes during meiosis. Due the recent divergence of the succulents I am interested in, there is usually little real difference in chromosome
structure, mostly just whole sets of doublings combined with the loss of one or two “extras” here and there. I would love to find some funding to do a comparative genomics paper in this area
eventually.

In the meanwhile I am hoping to experiment with inducing polyploidization in offsets fromSempervivum, Jovibarba, and Graptopetalum.
This is a common technique in commercial plant breeding and very safe even though the result is clearly a 'genetic modification' (the doubling of every gene in the plant and corresponding changes
in gene dosage). Not only that, but this doubling is done usually to produce fertile hybrids they can then use to move genes between species or genera. Why this technique doesn't count as GM is
beyond me but I digress...

My goal would be the creation of hybrid lines for myself and other breeders to use as tools to create new cultivars. Additionally I hope to one day sequence
the ‘metagenome’ of Crassulaceae. With that data and a comparative genome tool such as a gene chip I would be able to look closely at the genetic underpinnings of all this phenotypic
diversity.

I am interested in developing a mechanism (genetic or hormonal) of suppressing flowering in Sempervivum and other monocarpic members of
Crassulaceae as many enthusiasts are disappointed when their favorite rosette flowers and dies leaving a bare patch on their wall (especially if the plant hadn’t produced any offsets). I
plan to treat some of my plants with various cytokinins as a first step in this research. I would also like to use these plants to figure out how to induce fasciated or monstrose
forms.

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